Host Cell Contact Induces Expression of Virulence Factors and VieA, a Cyclic di-GMP Phosphodiesterase, in Vibrio cholerae

Abstract

Vibrio cholerae, a noninvasive bacterium, colonizes the intestinal epithelium and secretes cholera toxin (CT), a potent enterotoxin that causes the severe fluid loss characteristic of the disease cholera. In this study, we demonstrate that adherence of V. cholerae to the intestinal epithelial cell line INT 407 strongly induces the expression of the major virulence genes ctxAB and tcpA and the virulence regulatory gene toxT. No induction of toxR and tcpP, which encode transcriptional activators of toxT, was observed in adhered bacteria, and the adherence-dependent upregulation of toxT expression was independent of ToxR and TcpP. A sharp increase in the expression of the vieA gene, which encodes a cyclic di-GMP (c-di-GMP) phosphodiesterase, was observed in INT 407-adhered V. cholerae immediately after infection. Induction of toxT, ctxAB, and tcpA in INT 407-adhered vieA mutant strain O395 ⌬vieA was consistently lower than in the parent strain, although no effect was observed in unadhered bacteria, suggesting that VieA has a role in the upregulation of toxT expression specifically in host cell-adhered V. cholerae. Furthermore, though VieA has both a DNA binding helix-turn-helix domain and an EAL domain conferring c-di-GMP phosphodiesterase activity, the c-di-GMP phosphodiesterase activity of VieA is necessary and sufficient for the upregulation of toxT expression.

Staying Alive: Vibrio cholerae ’s Cycle of Environmental Survival, Transmission, and Dissemination

“…ToxT undergoes conformational changes depending on signals encountered in the stomach and small intestine; when in its active conformation ToxT promotes production of TCP and CT by binding directly to the tcpA and ctx promoter regions and displacing the nucleoid-associated protein, H-NS, which acts as a silencer of virulence gene expression (64, 207, 236). Experiments performed with the intestinal epithelial cell line INT 407 indicate that contact with host cells results in strong induction of major virulence genes ctxAB , tcpA, and toxT (Figure 6) (237). This response is triggered by strong induction of vieA , which encodes a phosphodiesterase that degrades c-di-GMP via its EAL domain; furthermore, the VieA’s EAL domain was required for induction of toxT in response to host cell contact (237).…”

“…Experiments performed with the intestinal epithelial cell line INT 407 indicate that contact with host cells results in strong induction of major virulence genes ctxAB , tcpA, and toxT (Figure 6) (237). This response is triggered by strong induction of vieA , which encodes a phosphodiesterase that degrades c-di-GMP via its EAL domain; furthermore, the VieA’s EAL domain was required for induction of toxT in response to host cell contact (237). These results indicate that host cell contact following mucosal penetration results in virulence gene expression.…”

The ins and outs of cyclic di-GMP signaling in Vibrio cholerae

“…Loss of the VieSAB system prevents full expression of the gene encoding key virulence regulator ToxT, as well as the genes encoding cholera toxin (CT) [48]. Contact with mammalian epithelial cells promotes expression of vieA, and the EAL domain of VieA was shown to be involved in depleting c-di-GMP levels and inducing virulence gene expression upon sensing host cell contact [49]. …”

Vibrio vulnificus infection induces the maturation and activation of dendritic cells with inflammatory Th17-polarizing ability

“…According to several studies, the upregulation of certain virulence factor-associated genes depends on the contact of host cells with pathogens (22,28). The expression of several virulence factors of V. vulnificus is significantly increased upon contact with host cells (29)(30)(31).…”